1. Field of the Invention
This invention relates generally to Tire Pressure Monitoring (TPM) systems, and specifically to autolocation of wheel units in a TPM system.
2. Description of the Prior Art
The tire pressure of motor vehicles should be kept within specified limits for both safety and efficiency reasons. TPM systems remotely monitor tire pressure and alert the vehicle user when a specified pressure threshold has been crossed. Hence the user is constantly aware of the condition of their vehicle tire pressures. The TPM systems typically include wheel units, one located in each wheel, which encode and broadcast pressure, temperature and a unique identifier via a wireless transmitter circuit, and a Radio Frequency (RF) receiver located on the vehicle which receives and decodes the pressure, temperature, and unique identifier information. The wheel unit sends messages to the central receiver concerning tire condition, such as tire pressure, and oftentimes tire temperature, and the user is alerted to the existence of the warning. Due to the unique identifier for each wheel unit, the user can be alerted to the location of the tire in which the error condition exists, hence improving diagnosis and repair of the error. It is common that during the lifetime of a tire it will be moved from one location to another on a vehicle e.g. when tires are rotated.